No, pushing the hard reset button causes a hardware reset. In terms of the potential damage to the filesystems, it is roughly analogous to a power failure. Most file systems are fairly resistant to such things, especially if they were quiescent at the time, and on the ensuring reboot, Unix should see that the file systems that were not properly unmounted are fscked to ensure they don't have severe errors.

I would never claim you can never corrupt a file system by power-cycling or resetting a machine, but Linux developers (along with OS developers of all ilks) realize these things happen and have taken pains to construct filesystems and order file system writes so that a reboot at a random point will not cause grievous damage. I run ext2 on my plug. If I hard reboot it, I typically see an fsck on reboot, and occasionally, if something is repaired by that fsck, an auto-re-reboot to start Linux on the repaired file system. I've never lost an ext2 fs to a random reboot. However, I'm certainly not issuing any warranties. YMMV.

restamp, Thank you. Well, I did not expect a loss of fs; but even a few files getting corrupted or loss is not really acceptable. So I have to always shut down the machine from a terminal first before unplugging cards!

It would be convenient to have an orderly power down mechanism from the switch at the Plug, since the Plug may be physically located away from a terminal.

One way, which even many hand-held devices do these days, is to have two modes of operation from the same push switch. A momentary push does an orderly shutdown; but holding it down for 3+ secs will activate the hard reset. To achieve that, the board needs to have a couple of gates with an (analog or digital) timer on board, this tiny circuit provides two outputs, a sw interrupt to the pc [the new one], and hard reset [the current one].

I wonder if this has been already implemented on our Plug board? If so, what is needed is some changes in the interrupt handling of the power down sequence for the momentary push.

I think the Plug was designed from the perspective that it is a server and, as such, is intended to be left powered on 24/7. It's not intended to be a PC, although with the right combination of USB devices, it certainly looks like it could be turned into one. Certainly, I wouldn't expect a recessed reset switch -- one that you need a paperclip to access -- would perform anything but a hard reset.